Plasma Spraying Process Optimization And Residual Stress Simulation Of Cr₂O₃-8TiO₂ Ceramic Coating

The plasma spraying has developped rapidly in the past decades. At present the researches mainly focus on the improving of spraying quality, stability, efficiency, etc.This subject aims to study the bonding strength of plasma sprayed Cr₂O₃—8TiO2 coating on 45 steel, to get the optimization parameters through the orthogonal experiment, and to analyze the main parameters that may affect the bonding strength. The bonding strength, hardness and porosity of coatings with different thickness are investigated, and the residual stress has analyzed by the help of computer simulation software MARC.The brief conclusions are stated as below:An orthogonal experiment was used to investigate the influence of spraying distance, electrical current, primary gas flow rate and secondary gas flow rate on the plasma spraying NiCrAl bonding coating and Cr₂O₃—8 TiO2 working coatings.The sequence of factors that affect the bonding strength of NiCrAl coatings is: primary gas flow rate, secondary gas flow rate, spraying distance and electrical current. The optimized coatings had a bonding strength of 76.6MPa, porosity of 0.42% and micro-hardness of 321Hv.The sequence of factors that affect the bonding strength of Cr₂O₃—8TiO2 coatings is: spraying distance, electrical current , secondary gas flow rate and primary gas flow rate. The optimized coatings had a bonding strength of 29.2MPa, porosity of 3.80% and micro-hardness of 2528Hv.Bonding coating can release the residual stress between the substrate and the ceramic coating. The ceramic's bonding strength can change from 15.0MPa to 29.2MPa by spraying a bonding coating on substrate instead of spraying a ceramic coating directly.According to the analysis of the coating's thickness between bonding strength, micro-hardness and porosity , the result is: bonding strength and micro-hardness decreased as coating's thickness increased, while porosity increased as coating's thickness increased A mathematical model is developed to simulate the residual stress of the coatings. It shows that, in bonding coating, the radial stress, axial stress and tangential stress are draw stress, and the radial stress is the most important factor; in ceramic coating, the radial stress, axial stress and tangential stress are press stress, and the radial stress is the most important factor.